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I required a circuit for calculating the speed of a DC motor. Is it possible to design a one like that? Please give your ideas and suggestions for this. I will attach datasheet of my DC motor.
What do you "have" in hands? You need to provide more information on pretty much everything.
Also you can try to search for "DC motor control" on the web.
To basically control the speed of a DC motor you typically need a RPM to voltage converter (you can make one by disassemble an old computer mouse with ball inside and the circuitry) and some circuit to vary the speed. The latter often consists of a PID controller and a switching voltage supply.
You need to generate a pulse or number of pulses for every turn of the motor spindle, then count the number of pulses generated over a fixed time period...then convert that to revolutions per minute...
Many dc motors can also be controlled using a purely analog circuit.
They work on the principle that the back emf voltage is related to
the speed of the shaft. The idea then is to create a circuit that
measures the back emf while the motor is running and then generate
a control signal based on the back emf and a reference signal.
Many older cassette tape decks used this kind of controller.
If you only need to 'measure' the speed then you can make a
circuit to measure the back emf and that will give you the
scaled speed measurement.
If you don't want to or have the time to make a tach circuit, buy a model airplane tach for 2 bladed prop from a radio control hobby shop. You just need to attach a B&W drawing (4 quadrants, alternating black and white, B_W_B_W) on the shaft to measure the RPM. In 1990 I paid about $40 for my tach.